Processing baths



1962 H. LAWSON-TANCRED 3,051,461

PROCESSING BATE-IS 2 Sheets-Sheet 1 Filed March 14, 1960 I lea U C] 1 .2 15 1 I 1 INVENTOR amma/Lad.

United States Patent Ofiice 3,051,461 Patented Aug. 28, 1962 3,051,461 PROCESSING BATHS Henry Lawson-Tancred, Wetherby, England, assignor to Tancred & Langley Limited, Leeds, England, a British company Filed Mar. 14, 1960, Ser. No. 14,606 Claims priority, application Great Britain Mar. 26, 1959 8 Claims. (Cl. 263-11) This invention relates to processing baths, such as galvanising baths, salt baths, tempering baths and the like, and particularly relates to the heating of such baths for heating the contents thereof.

Various methods have been employed for heating processing baths and generally hot products of combustion are vented directly into one or more chambers lying adjacent the walls of the bath. Moreover, it is customary to cover the bath externally with firebricks or other similar material. With known arrangements one main disadvantage is that the heat is not applied evenly to the bath with the result that one or more hot spots are created which is very detrimental and causes uneven heating of the bath contents. Moreover, the control of the temperature of the bath contents is difiicult in that often in processing operations it is necessary to ensure that the temperature of the bath contents does not rise above a critical degree and it has been found that due to the heat storage in the bath cover and/r setting the temperature can rise above the required limits.

The main object of the present invention is to provide an improved method of, and means for, heating processing baths and giving greater control of the temperature of the contents.

Accordingly there is'provided a method of heating a processing bath, consist-ing in pressurising heated gases in at least one plenum chamber and venting the gases therefrom in a multiplicity of streams of substantially equal velocity such that they impinge directly on to the bath wall area to be heated from close range to provide uniform heating thereof.

The invention includes a processing bath having at least one plenum chamber adjacent thereto, means for providing a predetermined pressure of heated gases in said chamber, vertical feed ducts rising from said chamber for impinging the gases in a multiplicity of streams directly on to the bathwall or walls at a required velocity for heating the bath contents, and means for returning the gases to the pressurising means for recirculation.

The invention will now be more particularly described with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of a rectangular bath provided with two plenum chambers and two heating-pressurising units;

FIG. 2 is a similar plan view to FIG. 1, but with the top covering units removed to expose the plenum chambers, feeding means and heating-pressurising units;

FIG. 3 is a sectional elevation on line XX of FIG. 2;

FIG. 4 is a sectional elevation on line YY of FIG. 2;

FIG. 5 is a detail elevation of a duct showing the feeding openings; and

FIG. 6 is a substantially diagrammatic plan view of a modified arrangement of two plenum chambers, for a rectangular bath.

As illustrated in FIGS. 1 to 5, a processing bath structure particularly suitable for galvanising purposes, includes a bath 1 of rectangular formation with two plenum chambers 2 which are of L-formation in plan view. These chambers are located at a low level in relation to the bath and well below the floor level 3. The plenum chambers 2 rest on a base raft 4 and the bath is raised on a base 5 whilst a surrounding wall 6 rises from the base raft; removable cover slabs 7 are provided for top closure purposes, with a removable or other superstructure 8 to complete the bath setting. This construction provides two gas passageways 2a each of which is bounded below by the top of a plenum chamber 2, above by the slabs 7, on the inner side by the wall of the bath 1 and on the outer side by the surrounding wall 6. Each passageway 2a is closed at one of its ends at 23 while its other end is open into one of the chambers 10.

At each end of the bath structure there is provided heating means 9 which are intended to illustrate gas or oil burner units although electrical heating means may be employed. Hot gases from units 9 are forced into the chambers 10 in which fan units 11 are mounted and provided with drive means 12 and electric motors 13. The fan units are adapted to draw hot gases from the chambers 10 and to force the hot gases through ducts 14 into the ends of the L-shaped plenum chambers 2.

The hot gases in the plenum chambers 2 rise through feeding ducts 15 which are upstanding on the top of the chambers with their inner walls lying parallel with the bath walls. These ducts are shown of rectangular crosssection, they may be of other section, and each has one wall 16 furnished with a fin 16a extending laterally to the bath wall and upward from the plenum chamber, and such ducts are spaced apart so that in effect there is an L-shaped space formed between each pair of ducts and each duct and the bath wall as viewed in plan (see FIG. 2). This L-shaped space is sealed oif at the bottom at 17 and also level with the top of the duct at 22 and between these two levels the inner wall of each duct is furnished with rows of holes 18 for impinging gases from the ducts directly on to the closely adjacent metallic wall of the bath. The gases from the ducts 15 after impinging on the bath wall pass out through the L-shaped spaces into the gas passageways 2a on the outside of the ducts and above the plenum chambers 2 and each passageway 2a is blanked off at 23 i.e. at the end thereof adjacent to the entry end of the plenum chamber lying beneath it so that hot gases must recirculate from each plenum chamber 2 back through its overlying passageway 2a to the chamber 10 of the other heating unit. In the above manner hot gases provided by one heating unit are recirculated by the other heating unit and thus there is a clockwise movement, or anticlockwise, according to the arrangement of the structure, of hot gases around the bath 1.

To obtain even velocity of the gases and amount to be circulated for a galvanising bath the rating of each fan can be calculated in any known circumstance. The main requirements for such calculations are to know the bath and the total amount of heat which must be applied to the bath to obtain a desired output in unit time.

The use of a multiplicity of holes 18 in each feeding duct 15 and the use of a plurality of equally-spaced closely-adjacent feed-ing ducts 15 arranged in close proximity to all the wall area of the bath to be heated, ensures even heating of the bath wall. Also, it has been found that substantially equal velocity from each of the feeding ducts 15 and holes 18 can be obtained by arranging the cross-sectional area of each plenum chamber 2 to be approximately one-and-a-half times the total cross-sectional area of all its feeding ducts 15 and arranging the cross-sectional area of each feeding duct 15 to be one and-a-h-alf times the area of all the venting holes 18 in such duct.

In the above arrangement the major part of the bath wall area is heated evenly and due to the fact that the gases are impinged at close range directly on to the metallic wall of the bath and immediately recirculated away therefrom, the heating means can be thermostatically controlled, and as there is no brick setting associated with such wall area and thus no heat storage, the temperature of the contents of the bath can be more accurately controlled than hitherto and there is no danger of the temperature of the bath rising above a critical degree. As shown, the hot gases are impinged on to the bath walls to a level terminating short of the bottom of the bath in a manner required for galvanising baths, although in some types of bath the venting of hot gases could be on to the whole of the wall area and also the bottom if desirable.

The arrangement of the plenum chambers may be modified to suit requirements and FIG. 6 diagrammatically illustrates another arrangement, wherein U-shaped plenum chambers 2b (in plan) are shown with centrally aligned hot gas inlet means "19 provided. Also, each plenum chamber 2b may include baffle means 20 for ensuring more even distribution of the hot gases.

Although only a rectangular bath has been shown it will be understood that the invention can be applied to baths of other shapes including circular or cylindrical and although it has been found more convenient to use two plenum chambers with individual heating-pressuring means, a single plenum chamber, or more than two such chambers, may be employed. Moreover, an underfloor exhaust ducting 291 isshown and this may have damper control means and is connected to an extraction fan. The total weight of gases removed by this extraction man must equal the sum of that induced into the system at the burner ends of the two combustion tubes for combustion gases. 7

What I claim is:

1. A processing bath comprising a vessel for the material to be heated, said vessel having an upstanding side wall, at least one plenum chamber extending horizontally alongand adjacent to the lower edge of said side wall, a plurality of feeding ducts extending upwardly from and communicating with said plenum chamber, said feeding ducts being spaced apart from and parallel to each other a and each having a wall spaced apart from and adjacent to said side wall of said vessel, said wall of each feeding duct which is adjacent to said side wall of said vessel being provided with venting openings for discharging hot gas against said side wall of said vessel, gas heating means, a second chamber into which hot gas is discharged from said heating means, means for drawing hot gas from said second chamber and delivering said hot gas under pressure into said plenum chamber, a gas passageway surrounding said feeding ducts'for collecting the gas emitted from said venting openings, said gas passageway com- I I; municating with said second chamber whereby the gas discharged from said feeding ducts is recirculated under pressure with fresh hot gas from said heating means.

2. A processing bath as defined in claim 1 comprising a fin extending upwardly from said plenum chamber and laterally from each feeding duct to said side wall.

3. A processing bath as defined in claim 1 comprising two plenum chambers in the same horizontal plane each provided with a series of upstanding feeding ducts, said plenum chambers extending along different portions of said side wall, means associated with each of said two plenum chambers for heating gas, forced draft means at an inlet end of each plenum chamber and associated with each heating means for drawing heated gas from its associated heating means and delivering it under pressure to its associated plenum chamber, a gas passageway enclosing the feeding ducts of each plenum chamber, the gas passageway surrounding the feeding ducts of one plenum chamber communicating with the forced draft means for drawing heated gas from the gas heating means associated with the other plenum chamber.

4. A processing bath as defined in claim 1 comprising an exhaust duct leading from said gas passageway.

5. A processing bath as defined in claim 3 in which said vessel is rectangular in plan and each plenum chamber is L-shaped in plan and extends along two sides of said vessel.

6. A processing bath as defined in claim 3 in which said vessel is rectangular in plan and each plenum chamber is U-shaped in plan and extends across one wall and partly along the two adjacent walls of said vessel.

' 7. A processing bath as defined in claim 1 in which the cross section of each plenum chamber is about one and one half times the total area of the cross sections of said feeding ducts and the cross section of each feeding duct is about one and one-half times the area of the venting openings therein.

8. A processing bath as defined in claim 1 in which the openings in each feeding duct are located adjacent a portion of said side Wall above the lower edge thereof.

References Cited in the file of this patent UNITED STATES PATENTS 

